Apparatus and method of avoiding control channel blocking

ABSTRACT

A method is provided of receiving a control channel at a user equipment in a wireless communication system. A subframe including a plurality of search spaces is received. Each of the plurality of search spaces is associated with a respective carrier indicator field (CIF) value. At least one control channel candidate for a cell indicated by a first CIF value is monitored in two or more of the plurality of search spaces for control channel candidates having a same downlink control information (DCI) format size and different CIF values.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of U.S. patent application Ser. No.14/081,384 filed on Nov. 15, 2013 (now U.S. Pat. No. 9,554,377 issued onJan. 24, 2017), which is a Continuation of U.S. patent application Ser.No. 13/513,072 filed on May 31, 2012 (now U.S. Pat. No. 8,634,374 issuedon Jan. 21, 2014), which is filed as the National Phase ofPCT/KR2010/009076 filed on Dec. 17, 2010, which claims the benefit under35 U.S.C. § 119(e) to U.S. Provisional Application Nos. 61/299,355 filedon Jan. 29, 2010, 61/293,211 filed on Jan. 8, 2010, and 61/287,700 filedon Dec. 17, 2009, all of which are hereby expressly incorporated byreference into the present application.

BACKGROUND OF THE INVENTION

Radio communication systems have been diversified in order to providevarious types of communication services such as voice or data services.In general, a radio communication system is a multiple access systemcapable of sharing available system resources (bandwidth, transmit poweror the like) so as to support communication with multiple users.Examples of the multiple access system include a Code Division MultipleAccess (CDMA) system, a Frequency Division Multiple Access (FDMA)system, a Time Division Multiple Access (TDMA) system, an OrthogonalFrequency Division Multiple Access (OFDMA) system, a Single CarrierFrequency Division Multiple Access (SC-FDMA) system, and the like.

SUMMARY OF THE INVENTION

The present invention is directed to a wireless communication system,particularly apparatus and method of avoiding control channel blocking.

An object of the present invention devised to solve the problem lies ona method and apparatus for avoiding control channel blocking in a radiocommunication system supporting carrier aggregation.

Another object of the present invention devised to solve the problemlies on a method and apparatus for efficiently performing blind decodingof a control channel.

A further object of the present invention devised to solve the problemlies on a method and apparatus for constructing a search space so as toefficiently transmit a control channel.

In a first aspect of the invention, a method of receiving a controlchannel at a user equipment in a wireless communication system usingmultiple carriers is provided, in which the method comprises: receivinga plurality of search spaces, wherein each search space comprises aplurality of control channel candidates and each search space iscorresponding to respective carrier; and monitoring the control channelcandidates for the control channel, wherein if the control channelcandidates have a common information size over two or more searchspaces, the control channel can be received via any one of the two ormore the search spaces.

In a second aspect of the invention, an user equipment adapted toreceive a control channel in a wireless communication system usingmultiple carriers is provided, in which the user equipment comprises: aradio frequency (RF) unit; and a processor, wherein the processor isadapted to receive a plurality of search spaces, wherein each searchspace comprises a plurality of control channel candidates and eachsearch space is corresponding to respective carrier, and to monitor thecontrol channel candidates for the control channel, wherein if thecontrol channel candidates have a common information size over two ormore search spaces, the control channel can be received via any one ofthe two or more the search spaces.

Preferably, if the control channel candidates have the commoninformation size over the two or more search spaces, the monitoring isperformed on an assumption that the control channel candidates havingthe common information size can be received via any one of the two ormore search spaces.

Preferably, the control channel candidates having the common informationsize are discriminated using CIF (Carrier Indicator Field) values.

Preferably, if the control channel candidates have different informationsizes over the plurality of search spaces, the control channel isreceived via only one search space that is corresponding to a carrierrelated with the control channel.

Preferably, the plurality of search spaces are received via a samecarrier, and the control channel includes a CIF (Carrier IndicatorField) value used for indicating a related carrier.

Preferably, the control channel is CRC (Cyclic Redundancy Check)scrambled with RNTI (Radio Network Temporary Identifier).

Preferably, the plurality of search spaces are user equipment specificsearch spaces.

Preferably, the information size includes a DCI (downlink controlinformation) payload size.

Preferably, the monitoring includes decoding each of the controlcandidates for the control channel.

Preferably, the above aspects further include performing an operation inaccordance with the control channel.

In a third aspect of the invention, a method of transmitting a controlchannel at a network node in a wireless communication system usingmultiple carriers is provided, in which the method comprises:constituting a plurality of search spaces, wherein each search spacecomprises a plurality of control channel candidates and each searchspace is corresponding to respective carrier; and transmitting thecontrol channel via the plurality of search spaces, wherein if thecontrol channel candidates have a common information size over two ormore search spaces, the control channel can be transmitted via any oneof the two or more search spaces.

In a fourth aspect of the invention, a network equipment adapted totransmit a control channel in a wireless communication system usingmultiple carriers is provided, the network equipment comprises: a radiofrequency (RF) unit; and a processor, wherein the processor is adaptedto constitute a plurality of search spaces, wherein each search spacecomprises a plurality of control channel candidates and each searchspace is corresponding to respective carrier, and to transmit thecontrol channel via the plurality of search spaces, wherein if thecontrol channel candidates have a common information size over two ormore search spaces, the control channel can be transmitted via any oneof the two or more search spaces.

Preferably, if the control channel candidates have the commoninformation size over the two or more search spaces, the control channelcandidates having the common information size can be transmitted via anyone of the two or more search spaces.

Preferably, the control channel candidates having the common informationsize are discriminated using CIF (Carrier Indicator Field) values.

Preferably, if the control channel candidates have different informationsizes over the plurality of search spaces, the control channel istransmitted via only one search space that is corresponding to a carrierrelated with the control channel.

Preferably, the plurality of search spaces are transmitted via a samecarrier, and the control channel includes a CIF (Carrier IndicatorField) value used for indicating a related carrier.

Preferably, the control channel is CRC (Cyclic Redundancy Check)scrambled with RNTI (Radio Network Temporary Identifier).

Preferably, the plurality of search spaces are user equipment specificsearch spaces.

Preferably, the information size includes a DCI (downlink controlinformation) payload size.

According to the present invention, it is possible to avoid controlchannel blocking in a radio communication system supporting carrieraggregation. In addition, it is possible to efficiently perform blinddecoding of a control channel. In addition, it is possible toefficiently constitute a search space.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 is a diagram showing an exemplary structure of a radio frame of a3^(rd) Generation Partnership Project (3GPP) system.

FIG. 2 is a diagram showing a resource grid for a downlink slot.

FIG. 3 is a diagram showing an exemplary structure of a downlink frame.

FIG. 4 is a flowchart illustrating a process of constituting a PDCCH ata base station (BS).

FIG. 5 is a flowchart illustrating a process of processing a PDCCH at auser equipment (UE).

FIG. 6 is a diagram showing an exemplary structure of an uplinksubframe.

FIG. 7 is a diagram showing a Carrier Aggregation (CA) communicationsystem.

FIG. 8 is a diagram showing cross-carrier scheduling.

FIG. 9 is a diagram showing a method of constituting search spacesaccording to an embodiment of the present invention.

FIG. 10 is a diagram showing a method of processing a control channelaccording to an embodiment of the present invention.

FIGS. 11A, 11B and 12 are diagrams showing examples of constitutingsearch spaces in the case where one monitoring DL CC is used, accordingto an embodiment of the present invention.

FIG. 13 is a diagram showing an example of constituting search spaces inthe case where a plurality of monitoring DL CCs is used, according to anembodiment of the present invention.

FIGS. 14 to 15 are diagrams showing examples of constituting searchspaces in the case where the number of times that blind decoding can beperformed is limited, according to an embodiment of the presentinvention.

FIG. 16 is a diagram showing an example of constituting search spacesusing DCI size unification according to an embodiment of the presentinvention.

FIGS. 17 to 20 are diagrams showing an example of a search space in acarrier aggregation state according to an embodiment of the presentinvention.

FIGS. 21 to 22 are diagrams showing simulation results when searchspaces are shared, according to an embodiment of the present invention.

FIG. 23 is a diagram illustrating a BS and a UE, which can be applied tothe embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following technologies may be utilized in various radio accesssystems such as a Code Division Multiple Access (CDMA) system, aFrequency Division Multiple Access (FDMA) system, a Time DivisionMultiple Access (TDMA) system, an Orthogonal Frequency Division MultipleAccess (OFDMA) system, or a Single Carrier Frequency Division MultipleAccess (SC-FDMA) system. The CDMA system may be implemented as radiotechnology such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. The TDMA system may be implemented as radio technology such asGlobal System for Mobile communications (GSM)/General Packet RadioService (GPRS)/Enhanced Data Rate for GSM Evolution (EDGE). The OFDMAsystem may be implemented as radio technology such as IEEE 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20 or E-UTRA (Evolved UTRA). TheUTRA system is part of the Universal Mobile Telecommunications System(UMTS) standard. A 3^(rd) Generation Partnership Project Long TermEvolution (3GPP LTE) communication system is part of the E-UMTS (EvolvedUMTS) standard, which employs an OFDMA system in downlink and employs anSC-FDMA system in uplink. LTE-A (Advanced) is an evolved version of 3GPPLTE.

In order to clarify the description, the 3GPP LTE/LTE-A will be focusedupon, but the technical scope of the present invention is not limitedthereto. It should be noted that specific terms disclosed in the presentinvention are proposed for convenience of description and betterunderstanding of the present invention and these terms may be replacedwith other terms within the technical scope or spirit of the presentinvention.

FIG. 1 shows an exemplary structure of radio frame.

Referring to FIG. 1, a radio frame includes 10 subframes. A subframeincludes two slots in time domain. A time for transmitting one subframeis defined as a transmission time interval (TTI). For example, onesubframe may have a length of 1 millisecond (ms), and one slot may havea length of 0.5 ms. One slot includes a plurality of orthogonalfrequency division multiplexing (OFDM) symbols in time domain. Since the3GPP LTE uses the OFDMA in the downlink, the OFDM symbol is forrepresenting one symbol period. The OFDM symbol may also be referred toas an SC-FDMA symbol or a symbol period. A resource block (RB) is aresource allocation unit, and includes a plurality of contiguoussubcarriers in one slot. The structure of the radio frame is shown forexemplary purposes only. Thus, the number of subframes included in theradio frame or the number of slots included in the subframe or thenumber of OFDM symbols included in the slot may be modified in variousmanners.

FIG. 2 shows a resource grid for one downlink slot.

Referring to FIG. 2, a downlink slot includes a plurality of OFDMsymbols in time domain. It is described herein that one downlink slotincludes 7 OFDM symbols, and one resource block (RB) includes 12subcarriers in frequency domain as an example. However, the presentinvention is not limited thereto. Each element on the resource grid isreferred to as a resource element (RE). One RB includes 12×7 REs. Thenumber N^(DL) of RBs included in the downlink slot depends on a downlinktransmit bandwidth. The structure of an uplink slot may be same as thatof the downlink slot.

FIG. 3 shows an exemplary structure of downlink structure.

Referring to FIG. 3, a maximum of three OFDM symbols located in a frontportion of a first slot within a subframe correspond to a control regionto be assigned with a control channel. The remaining OFDM symbolscorrespond to a data region to be assigned with a physical downlinkshared chancel (PDSCH). Examples of downlink control channels used inthe 3GPP LTE includes a physical control format indicator channel(PCFICH), a physical downlink control channel (PDCCH), a physical hybridARQ indicator channel (PHICH), etc. The PCFICH is transmitted at a firstOFDM symbol of a subframe and carries information regarding the numberof OFDM symbols used for transmission of control channels within thesubframe. The PHICH is a response of uplink transmission and carries anHARQ acknowledgment (ACK)/negative-acknowledgment (NACK) signal. Controlinformation transmitted through the PDCCH is referred to as downlinkcontrol information (DCI). The DCI includes uplink or downlinkscheduling information or includes an uplink transmit (Tx) power controlcommand for arbitrary UE groups.

The PDCCH may carry a transport format and a resource allocation of adownlink shared channel (DL-SCH), resource allocation information of anuplink shared channel (UL-SCH), paging information on a paging channel(PCH), system information on the DL-SCH, a resource allocation of anupper-layer control message such as a random access response transmittedon the PDSCH, a set of Tx power control commands on individual UEswithin an arbitrary UE group, a Tx power control command, activation ofa voice over IP (VoIP), etc. A plurality of PDCCHs can be transmittedwithin a control region. The UE can monitor the plurality of PDCCHs. ThePDCCH is transmitted on an aggregation of one or several consecutivecontrol channel elements (CCEs). The CCE is a logical allocation unitused to provide the PDCCH with a coding rate based on a state of a radiochannel. The CCE corresponds to a plurality of resource element groups(REGs). A format of the PDCCH and the number of bits of the availablePDCCH are determined according to a correlation between the number ofCCEs and the coding rate provided by the CCEs. The BS determines a PDCCHformat according to a DCI to be transmitted to the UE, and attaches acyclic redundancy check (CRC) to control information. The CRC is maskedwith a unique identifier (referred to as a radio network temporaryidentifier (RNTI)) according to an owner or usage of the PDCCH. If thePDCCH is for a specific UE, a unique identifier (e.g., cell-RNTI(C-RNTI)) of the UE may be masked to the CRC. Alternatively, if thePDCCH is for a paging message, a paging indicator identifier (e.g.,paging-RNTI (P-RNTI)) may be masked to the CRC. If the PDCCH is forsystem information (more specifically, a system information block (SIB)to be described below), a system information identifier and a systeminformation RNTI (SI-RNTI) may be masked to the CRC. To indicate arandom access response that is a response for transmission of a randomaccess preamble of the UE, a random access-RNTI (RA-RNTI) may be maskedto the CRC.

A PDCCH carries a message known as Downlink Control Information (DCI),which includes resource assignments and other control information for aUE or group of UEs. In general, several PDCCHs can be transmitted in asubframe. Each PDCCH is transmitted using one or more so-called ControlChannel Elements (CCEs), where each CCE corresponds to nine sets of fourphysical resource elements known as Resource Element Groups (REGs). FourQPSK symbols are mapped to each REG. The resource elements occupied byreference symbols are not included within the REGs, which means that thetotal number of REGs in a given OFDM symbol depends on whether or notcell-specific reference signals are present. The concept of REGs (i.e.mapping in groups of four resource elements) is also used for the otherdownlink control channels (the PCFICH and PHICH). Four PDCCH formats aresupported, as listed in Table 1.

TABLE 1 Number Number Number PDCCH format of CCEs (n) of REGs of PDCCHbits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

CCEs are numbered and used consecutively, and, to simplify the decodingprocess, a PDCCH with a format consisting of n CCEs may only start witha CCE with a number equal to a multiple of n. The number of CCEs usedfor transmission of a particular PDCCH is determined by the base stationaccording to the channel conditions. For example, if the PDCCH isintended for a UE with a good downlink channel (e.g. close to the basestation), then one CCE is likely to be sufficient. However, for a UEwith a poor channel (e.g. near the cell border) then eight CCEs may berequired in order to achieve sufficient robustness. In addition, thepower level of a PDCCH may be adjusted to match the channel conditions.

The approach adopted for LTE is to define for each UE a limited set ofCCE locations where a PDCCH may be placed. The set of CCE locations inwhich the UE may find its PDCCHs can be considered as a ‘search space’.In LTE the search space is a different size for each PDCCH format.Moreover, separate dedicated (UE-specific) and common search spaces aredefined, where a dedicated search space is configured for each UEindividually, while all UEs are informed of the extent of the commonsearch space. Note that the dedicated and common search spaces mayoverlap for a given UE. With such small search spaces it is quitepossible in a given subframe that the base station cannot find CCEresources to send PDCCHs to all the UEs that it would like to, becausehaving assigned some CCE locations the remaining ones are not in thesearch space of a particular UE. To minimize the possibility of suchblocking persisting into the next subframe, a UE-specific hoppingsequence is applied to the starting positions of the dedicated searchspaces. The sizes of the common and dedicated search spaces are listedin Table 2.

TABLE 2 Number of CCEs Number of candidates Number of candidates PDCCHformat (n) in common search space in dedicated search space 0 1 — 6 1 2— 6 2 4 4 2 3 8 2 2

In order to keep under control the computational load arising from thetotal number of blind decoding (BD) attempts, the UE is not required tosearch for all the defined DCI formats simultaneously. Typically, in thededicated search space, the UE will always search for Formats 0 and 1A,which are both the same size and are distinguished by a flag in themessage. In addition, a UE may be required to receive a further format(i.e. 1, 1B or 2, depending on the PDSCH transmission mode configured bythe base station). In the common search space the UE will search forFormats 1A and 1C. In addition the UE may be configured to search forFormat 3 or 3A, which have the same size as formats 0 and 1A, and may bedistinguished by having the CRC scrambled by a different (common)identity, rather than a UE-specific one. The transmission mode forconfiguring the multi-antenna technique and the information content ofthe different DCI formats are listed below.

Transmission Mode

-   -   Transmission Mode 1: Transmission from a single base station        antenna port    -   Transmission Mode 2: Transmit diversity    -   Transmission Mode 3: Open-loop spatial multiplexing    -   Transmission Mode 4: Closed-loop spatial multiplexing    -   Transmission Mode 5: Multi-user MIMO    -   Transmission Mode 6: Closed-loop rank-1 precoding    -   Transmission Mode 7: Transmission using UE-specific reference        signals

DCI Format

-   -   Format 0: Resource grants for the PUSCH transmissions (uplink)    -   Format 1: Resource assignments for single codeword PDSCH        transmissions (transmission modes 1, 2 and 7)    -   Format 1A: Compact signaling of resource assignments for single        codeword PDSCH (all modes)    -   Format 1B: Compact resource assignments for PDSCH using        rank-1-closed loop precoding (mode 6)    -   Format 1C: Very compact resource assignments for PDSCH (e.g.        paging/broadcast system information)    -   Format 1D: Compact resource assignments for PDSCH using        multi-user MIMO (mode 5)    -   Format 2: Resource assignments for PDSCH for closed-loop MIMO        operation (mode 4)    -   Format 2A: Resource assignments for PDSCH for open-loop MIMO        operation (mode 3)    -   Formats 3/3A: Power control commands for PUCCH and PUSCH with        2-bit/1-bit power adjustments

Considering the above, the UE would be required to carry out a maximumof 44 BDs in any subframe. This does not include checking the samemessage with different CRC values, which requires only a smalladditional computational complexity.

FIG. 4 is a flowchart illustrating a process of constituting a PDCCH ata base station (BS).

Referring to FIG. 4, the BS generates control information according to aDCI format. The BS may select one from among a plurality of availableDCI formats (DCI formats 1, 2, . . . , and N) according to controlinformation to be transmitted to a UE. In step S410, a Cyclic RedundancyCheck (CRC) for error detection is attached to the control informationgenerated according to each DCI format. The CRC is masked with a RadioNetwork Temporary Identifier (RNTI) according to an owner or usage of aPDCCH. In other words, the PDCCH is CRC-scrambled with an identifier(e.g., an RNTI).

Table 3 shows an example of identifiers masked to the PDCCH.

TABLE 3 Type Identifier Description UE-specific C-RNTI, used for aunique UE identification temporary C- RNTI, semi- persistent C-RNTICommon P-RNTI used for paging message SI-RNTI used for systeminformation RA-RNTI used for random access response

If a C-RNTI, a temporary C-RNTI or a semi-persistent C-RNTI is used, thePDCCH carries control information for a specific UE and, if the otherRNTI is used, the PDCCH carries common control information received byall UEs within a cell. In step S420, channel coding is performed withrespect to the control information to which the CRC is attached so as togenerate coded data. In step S430, rate matching according to a CCEaggregation level assigned to a PDCCH format is performed. In step S440,the coded data is modulated so as to generate modulation symbols. TheCCE aggregation level of the modulation symbols constituting one PDCCHmay be any one of 1, 2, 4 and 8. In step S450, the modulation symbolsare mapped to physical Resource Elements (RE).

FIG. 5 is a flowchart illustrating a method of processing a PDCCH at auser equipment (UE).

Referring to FIG. 5, in step S510, the UE demaps physical REs from CCEs.In step S520, since the UE does not know the CCE aggregation level ofthe received PDCCH, the UE performs demodulation at each CCE aggregationlevel. In step S530, the UE performs rate dematching with respect to thedemodulated data. Since the UE does not know the DCI format (or DCIpayload size) of the received control information, rate dematching isperformed with respect to DCI formats (or DCI payload sizes). In stepS540, channel decoding is performed with respect to the rate-dematcheddata according to a code rate and a CRC is checked so as to detecterrors. If no errors are detected, it means the UE detects its ownPDCCH. If an error is detected, the UE continuously performs blinddecoding with respect to the other CCE aggregation levels or the otherDCI formats (or DCI payload sizes). In step S550, the UE which detectsits own PDCCH removes the CRC from the decoded data so as to acquirecontrol information.

A plurality of PDCCHs for a plurality of UEs may be transmitted within acontrol region of the same subframe. The BS does not provide the UE withinformation indicating where the PDCCH is located in the control region.Accordingly, the UE monitors a set of PDCCH candidates within thesubframe and finds its own PDCCH. The term “monitoring” means that theUE attempts to decode the received PDCCH candidates according torespective DCI formats. This is referred to as blind decoding (blinddetection). Through blind decoding, the UE simultaneously performsidentification of the PDCCH transmitted to the UE and decoding of thecontrol information transmitted through the corresponding PDCCH. Forexample, in the case where the PDCCH is demasked using the C-RNTI, noCRC error detection means that the UE detects its own PDCCH.

In order to reduce overhead of blind decoding, the number of DCI formatsis set to be less than the number of types of control informationtransmitted using the PDCCH. The DCI format includes a plurality ofdifferent fields. The type of the field, the number of fields, and thebit number of each field varies according to the DCI format. Inaddition, the size of the control information matched to the DCI formatvaries according to the DCI format. A certain DCI format may be used fortransmission of two types of control information.

Table 4 shows an example of control information transmitted by DCIFormat 0. The lengths in bits of the following fields are exemplary andnonlimiting.

TABLE 4 Field bit(s) (1) Flag for format0/format1A differentiation 1 (2)Hopping flag 1 (3) Resource block assignment and [log₂(N_(RB)^(UL)(N_(RB) ^(UL) + 1)/2)] hopping resource Allocation (4) Modulationand coding scheme and 5 redundancy Version (5) New data indicator 1 (6)TPC command for scheduled PUSCH 2 (7) Cyclic shift for DM RS 3 (8) ULindex (TDD) 2 (9) CQI request 1

A flag field serves to differentiate Format 0 from Format 1A. That is,DCI Formats 0 and 1A have the same payload size and are differentiatedby the flag field. The length in bits of a resource block assignment andhopping resource allocation field may vary according to a hopping PUSCHor a non-hopping PUSCH. The resource block assignment and hoppingresource allocation field for the non-hopping PUSCH provides┌log₂(N_(RB) ^(UL)(N_(RB) ^(UL)+1)/2)┐ bits to resource allocation of afirst slot within an uplink subframe. N_(RB) ^(UL) denotes the number ofRBs included in an uplink slot and depends on an uplink transmissionbandwidth set in a cell. Accordingly, the payload size of DCI Format 0may vary according to uplink bandwidth. DCI Format 1A includes a fieldfor PDSCH assignment and the payload size of DCI Format 1A may varyaccording to downlink bandwidth. The DCI format 1A provides a referenceinformation bit size to DCI format 0. Accordingly, if the number ofinformation bits of DCI Format 0 is less than the number of informationbits of DCI Format 1A, “0” is attached to DCI Format 0 until the payloadsize of DCI Format 0 becomes equal to the payload size of DCI Format 1A.A padding field of the DCI format is filled with “0”.

FIG. 6 is a diagram showing an exemplary structure of an uplink subframeused in an LTE system.

Referring to FIG. 6, the uplink subframe includes a plurality of slots(e.g., two). Each slot may include SC-FDMA symbols, the number of whichvaries according to the length of a CP. For example, in the case of anormal CP, a slot may include seven SC-FDMA symbols. An uplink subframeis divided into a data region and a control region in a frequencyregion. The data region includes a PUSCH and is used to transmit a datasignal such as voice. The control region includes a PUCCH and is used totransmit control information. The PUCCH includes an RB pair (e.g., m=0,1, 2, 3) located at both ends of the data region on the frequency axisand hops between slots. The control information includes HARQ ACK/NACK,Channel Quality Information (CQI), Precoding Matrix Indicator (PMI) andRank Indication (RI).

FIG. 7 is a diagram showing a Carrier Aggregation (CA) communicationsystem.

Referring to FIG. 7, a plurality of uplink/downlink Component Carriers(CCs) may be aggregated so as to support a wider uplink/downlinkbandwidth. The CCs may be contiguous or non-contiguous in a frequencyregion. The bandwidths of the CCs are independently set. Asymmetric CAin which the number of UL CCs and the number of DL CCs are different isalso possible. The control information may be set to betransmitted/received only through a specific CC. Such a specific CC maybe referred to as a primary CC and the remaining CCs may be referred toas secondary CCs. For example, if cross-carrier scheduling (or cross-CCscheduling) is applied, a PDCCH for downlink assignment may betransmitted through DL CC#0 and a corresponding PDSCH may be transmittedthrough DL CC#2. The term “CC” may be replaced with other equivalentterms (e.g., carrier, cell and the like).

For cross-CC scheduling, the introduction of carrier indicator field(CIF) can be considered. Configuration for presence or absence of theCIF within PDCCH can be semi-statically and UE-specifically (or UEgroup-specifically) enabled by higher layer signaling (e.g., RRCsignaling). The baseline of PDCCH transmission is summarized as below.

-   -   CIF disabled: PDCCH on a DL CC assigns PDSCH resources on the        same DL CC and PUSCH resources on a single linked UL CC        -   No CIF        -   Same as LTE PDCCH structure (same coding, same CCE-based            resource mapping) and DCI formats    -   CIF enabled: PDCCH on a DL CC can assign PDSCH or PUSCH        resources in one of multiple aggregated DL/UL CCs using the CIF        -   LTE DCI formats extended with the CIF

CIF (if configured) is a fixed x-bit field (e.g., x=3)

CIF (if configured) location is fixed irrespective of DCI format size

-   -   Reusing LTE PDCCH structure (same coding, same CCE-based        resource mapping)    -   Cross-CC resource assignments can be configured both when the        DCI formats have the same or different sizes

Explicit CIF for the case of same DCI format size

It would be determined whether the CIF is included or not in cases theDCI format sizes are different

-   -   There will be an upper limit on the total number of BDs

In the case of presence of CIF, desirably, the base station may assignthe PDCCH monitoring DL CC set for reduction of BD complexity at the UEside. This CC set is a portion of the entire aggregated DL CCs and theUE only performs detection/decoding of PDCCHs scheduled for it on thisset. In other words, to schedule PDSCH/PUSCH for a UE, the base stationtransmits PDCCHs only through the PDCCH monitoring DL CC set. The PDCCHmonitoring DL CC set may be set UE-specific or UE-group-specific orcell-specific.

FIG. 8 shows an example of DL subframe for which 3 DL CCs areaggregated, and DL CC A is configured as the PDCCH monitoring DL CC. Ifthe CIF is disabled, each DL CC can transmit only the PDCCH schedulingPDSCH of each DL CC without the CIF, by following the LTE PDCCHprinciple. On the other hand, if the CIF is enabled by UE-specific (orUE-group-specific or cell-specific) higher layer signaling, only DL CC Acan transmit the PDCCHs scheduling not only PDSCH of DL CC A but alsoPDSCHs of the other CCs, by using the CIF. Note that no PDCCH istransmitted on DL CC B and C which are not configured as the PDCCHmonitoring DL CC. The term “PDCCH monitoring DL CC” can be replaced withequivalent terms such as a monitoring carrier, a monitoring cell, aserving carrier, a serving cell.

EXAMPLE

If cross-scheduling is not set in the CA system, a PDCCH for a specificcarrier is transmitted only via the corresponding carrier. For example,referring to FIG. 7, if non-cross-CC scheduling is set, a PDCCH for DLCC0/UL CC0 is transmitted only via DL CC0. Accordingly, only a PDCCHsearch space for DL CC0/UL CC0 is present in DL CC0. That is, a PDCCHsearch space is constituted per carrier and each PDCCH search space istransmitted only via the corresponding DL CC.

However, as shown in FIG. 8, if cross-CC scheduling is set (that is, CIFis enabled), the monitoring DL CC must transmit not only a PDCCHassociated with the monitoring DL CC but also PDCCHs associated with theother carriers. That is, the monitoring DL CC (DL CC A) must transmitall PDCCHs associated with DL CC A, DL CC B and DL CC C. Accordingly,the monitoring DL CC (DL CC A) must include a PDCCH search spaceassociated with DL CC A, a PDCCH search space associated with DL CC Band a PDCCH search space associated with DL CC C. If CIF is set asdescribed above, since a plurality of PDCCH search spaces must bedefined in one DL CC, PDCCH blocking due to limited PDCCH resources andincrease in the number of times that blind decoding is performed mayoccur. PDCCH blocking means that PDCCH scheduling for the correspondingcarrier is limited due to limited PDCCH resources. For example, if aplurality of PDCCH search spaces is defined in one carrier, availableresources of the PDCCH search space corresponding to each carrier may belimited due to limited PDCCH resources and thus a PDCCH assignmentlocation may be limited or PDCCH assignment may be impossible.

Accordingly, if CIF is set, there is a need for a method of solvingPDCCH blocking and blind decoding times increase. To this end, in themonitoring DL CC, the PDCCH search space may be newly defineddifferently from the conventional method. That is, the PDCCH searchspace may be newly defined to suit management of cross-CC scheduling.For example, the PDCCH search space may be defined over a plurality ofcarriers. However, if the PDCCH search space is newly defined, backwardcompatibility with the conventional system (e.g., LTE) is problematic.Moreover, since the payload size of the conventional DCI variesaccording to the carrier band even in the same format, the DCI structureneeds to be changed in order to define DCIs within the unified PDCCHsearch space.

For this reason, the present invention proposes a method of solvingPDCCH blocking and reducing the number of times that blind decoding isperformed on the assumption that the PDCCH search space is defined on aper carrier basis. In more detail, the present invention proposes amethod of constituting search spaces for blind decoding if a pluralityof CCs is aggregated and cross-CC scheduling is possible. Cross-CCscheduling may be performed using CIF inserted into a PDCCH.

Hereinafter, the embodiment of the present invention will be describedin detail with reference to the drawings. As described above, thetransmission modes of the aggregated CCs may be independently set andthe bandwidths of the CCs may be assigned per CC and thus may be thesame or different from each other. Among all CCs aggregated per UE(group), one or a plurality of DL CCs may be set to a PDCCH monitoringDL CC for the UE (group). The PDCCH monitoring DL CC is arbitrarilydefined in order to indicate a DL CC used to transmit a plurality ofPDCCH search spaces corresponding to carriers upon cross-CC scheduling.The PDCCH monitoring DL CC may be replaced with other equivalent terms.For example, the term “PDCCH monitoring DL CC” can be replaced withequivalent terms such as a monitoring carrier, a monitoring cell, aserving carrier, a serving cell.

For convenience, although PDSCH scheduling of DL CCs is shown in thedrawings, the present invention is equally applicable to PUSCHscheduling of UL CCs linked with DL CCs. For convenience, although a CCEaggregation level of 1 is shown in the drawings, the present inventionis equally or similarly applicable to the case where the CCE aggregationlevel has other values (e.g., 2, 4, or 8). Although it is assumed thatBDs for two DCI formats per PDCCH candidate can be performed similar tothe conventional LTE system with respect to all cases in the presentinvention, BDs for one or three or more DCI formats per PDCCH candidatemay be performed. For convenience, although symmetric CA in which thenumber of DL CCs and the number of UL CCs are the same is shown in thedrawings, the present invention is equally or similarly applicable toasymmetric CA in which the number of DL CCs and the number of UL CCs aredifferent. For convenience, although the case where DL CCs and UL CCsare linked in one-to-one correspondence is shown, the present inventionis equally or similarly applicable to the case where DL CCs and UL CCsare linked in many-to-one correspondence or one-to-many correspondence.

Embodiment 1: Search space construction according to information (e.g.,DCI)

In the present method, if cross-carrier scheduling is possible in astate in which a plurality of carriers is aggregated, search spaceshaving control information having the same size are shared. In otherwords, search spaces having control information having the same size areaggregated as opposed to being divided on a per carrier basis.Accordingly, monitoring of control information having the same size inthe control information associated with carriers may be performed withinthe same unified search space. In contrast, search spaces for controlinformation having different sizes are divided on a per carrier basis.Accordingly, monitoring of control information having different sizes inthe control information associated with carriers is performed onlywithin the search space corresponding to the corresponding carrier.

According to the present method, if search spaces having controlinformation having the same size are present, the sizes of the searchspaces for monitoring the control information may be set to be large.Accordingly, it is possible to increase freedom in control channelscheduling and to solve control channel blocking.

FIG. 9 is a diagram showing a method of transmitting a control channelto a specific UE at a BS.

Referring to FIG. 9, the BS constitutes a plurality of search spaces(S910). Each search space includes a plurality of control channelcandidates and is defined per carrier (e.g., CC). The definition of thesearch spaces per CC may be performed according to the PDCCH searchspace constitution method of the conventional LTE system. A parameter(e.g., a hashing pattern, a location, a size, etc.) for a search spaceper CC may be obtained by a combination of a parameter for a PDCCHsearch space of the conventional LTE system and a CIF value.

The plurality of search spaces includes a UE-specific search space or acommon search space and preferably includes a UE-specific search space.The control channel includes a PDCCH, and a control channel candidateincludes a PDCCH candidate. The control channel carries a variety ofcontrol information and a variety of control information formats ispresent according to the type/content of the control information.Thereafter, the BS transmits the control channel for the specific UE viathe plurality of search spaces (S920). The control channel (or thecontrol information) may carry an identifier in order to indicate thespecific UE. The identifier includes an RNTI, e.g., C-RNTI or SPS-RNTI.The control channel (or the control information) may be scrambled usingthe identifier. For example, the BS may transmit the PDCCH that isCRC-scrambled with the C-RNTI to the UE.

If cross-carrier scheduling is set, the plurality of search spaces isconstituted on the same DL CC. Cross-carrier scheduling may be performedusing the CIF within the control channel. The CIF may have arepresentative value (e.g., DL CC indication value) indicating a linkedDL/UL CC pair or a value separately indicating DL CC or UL CC. The CIFmay be represented by an absolute index or a relative index (e.g.,offset).

The search spaces may be constituted per linked DL/UL CC pair, DL CC orUL CC. The search spaces may be contiguous in a logical index or may beindependently set and the search spaces may partially or wholly overlapeach other. The size of the search space corresponding to each carrier(or CIF) may be determined in proportion to a maximum number of PDCCHstransmittable via the search space or may be given weights or all thesizes of the search spaces may be the same. One control informationformat per DL CC or UL CC may be set or two or more control informationformats per DL CC or UL CC may be set, in the search space correspondingto each carrier (or CIF). A DL/UL common control information format suchas DCI Format 0/1A of the LTE system may be set in the search spaces.The type of the control information format set in the search spaces mayvary according to the transmission mode (e.g., a MIMO mode).

When the search spaces are constructed, if control channel formatshaving the same size (or control information having the same sizeirrespective of the format) are present in the plurality of searchspaces, the search spaces of the corresponding control channel formatsare shared. If the number of search spaces constituted on one carrier isM (M≥2), N (N≤M) search spaces may be shared. The sharing/non-sharing ofthe search spaces or the number of search spaces may be determined percontrol channel format (or per control information size irrespective ofthe format). Accordingly, if the search spaces are constituted percarrier but the control formats having the same size (or the controlinformation having the same size irrespective of the format) arepresent, the search spaces are unified. In this case, a control channelfor the UE that is related with one of carriers (or CIF) correspondingto the shared N search spaces may be transmitted via any one of the Nsearch spaces. That is, control channel candidates having the same sizeover the N search spaces may be transmitted via any one of the N searchspaces. In this case, control channel candidates having the same sizeare discriminated using CIF (Carrier Indicator Field) values.

In contrast, if the sizes of the control channel formats are differentper search space, the search spaces of the control channel formats arenot shared. In this case, the control channel for the UE may betransmitted only via the search spaces corresponding to thecorresponding carrier (or CIF). That is, control channel candidates witha same CIF are transmitted via only one search space corresponding tothe CIF.

For example, the BS may constitute the search spaces per CC and comparethe DCI (format) sizes for all the CCs. If DCIs (formats) having thesame size are present, the BS may unify the search spaces of the DCIs(formats) so as to constitute an extended search space. Accordingly,PDCCHs for the DCIs (formats) having the same size may be transmittedvia any PDCCH candidate within the extended search space, instead of viarespective search spaces. In this case, PDCCH candidates within theextended search space are discriminated using CIF (Carrier IndicatorField) values.

FIG. 10 is a diagram showing an example of processing a control channel(e.g., a PDCCH) at a UE. The process of FIG. 10 corresponds to theprocess of FIG. 9 and the detailed description refers to the descriptionof FIG. 9.

Referring to FIG. 10, the UE receives a plurality (M: M≥2) of searchspaces (S1110). Each search space is defined per carrier. Thereafter,the UE monitors control channel candidates within the search spaces inorder to find a control channel assigned to the UE (S1120). Themonitoring process includes blind decoding each of the control channelcandidates. Thereafter, the UE may perform an operation according to thecontrol channel assigned to the UE (S1130).

At this time, if the control channel candidates have the sameinformation size over N (N≤M) search spaces, a control channel for theUE that is related with one of carriers (or CIF) corresponding to the Nsearch spaces may be received via any one of the N search spaces. Thus,the UE monitors control channel candidates on an assumption that thecontrol channel candidates having the same information size can bereceived via any one of the N search spaces. In this case, the controlchannel candidates having the same information size are discriminatedusing CIF (Carrier Indicator Field) values.

In contrast, if the control channel candidates have differentinformation sizes per search spaces, the control channel for thespecific UE may be received only via the search space corresponding tothe corresponding carrier (or CIF). That is, control channel candidateswith a same CIF are transmitted via only one search space correspondingto the CIF.

FIG. 11A shows an example of constituting search spaces according to anembodiment of the present invention. In the present example, three DLCCs are aggregated and the transmission modes of DL CCs are set to 1, 3and 4. For convenience, it is assumed that the bandwidths of all CCs arethe same and DL CC #1 is a PDCCH monitoring DL CC. Although the numberof times that BD is performed per DCI format is the same (BD isperformed with respect to six PDCCH candidates similar to the LTEsystem) in the present example, the number of times that BD is performedmay vary according to DCI formats.

Referring to FIG. 11A, the BS constitutes the search spaces per CC andcompares the DCI format sizes for all CCs. As a result of thiscomparison, the sizes of DCI Formats 1A for three DL CCs are the sameand DCI Formats 1, 2A and 2 respectively have different sizes.Accordingly, the BS unifies three search spaces for DCI Format 1A(search space sharing). Accordingly, the BS may transmit DCI Format 1A(CIF=DL CC #1) via the PDCCH candidate of any one of a search space forDL CC #1, a search space for DL CC #2 and a search space for DL CC #3.Similarly, DCI Format 1A (CIF=DL CC #2) and DCI Format 1A (CIF=DL CC #3)may be transmitted via the PDCCH candidate of any one of three searchspaces. That is, DCI Format 1A candidates (CIF=DL CC #1, #2 or #3) canbe transmitted via any one of search spaces for DL CC #1, #2 and #3.Thus, UE monitors PDCCH candidates on an assumption that DCI Format 1Acandidates (CIF=DL CC #1, #2 or #3) can be received via any one ofsearch spaces for DL CC #1, #2 and #3. In this case, DCI Format 1Acandidates are discriminated using CIF values.

In contrast, since the DCI formats 1, 2A and 2 respectively have uniquesizes, the search spaces for the DCI formats 1, 2A and 2 are not sharedand are managed per CC. That is, DCI Format 1 (CIF=DL CC #1) may betransmitted only via the search space corresponding to DL CC #1.Similarly, DCI Format 2A (CIF=DL CC #2) and DCI Format 2 (CIF=DL CC #3)may be transmitted only via the search spaces corresponding to DL CC #2and DL CC #3, respectively.

The following detailed description will take into consideration that themaximum BD times (MaxBD) may be limited. MaxBD=36 indicates that thenumber of times that BD is performed is not reduced compared with beforethe search spaces are shared. In the case of MaxBD=36, the BD for DCIFormat 1A may be commonly performed via the search spaces including 18(=6×3) PDCCH candidates of the unified and extended search space. Incontrast, the BD for DCI Formats 1, 2A and 2 is performed via the searchspaces including six PDCCH candidates.

If MaxBD is reduced to 24, the number of times that BD is performed perDCI format must be reduced. If it is assumed that the number of timesthat BD is performed per DCI format is held constant, the number oftimes that BD is performed per DCI format is reduced to 4 (=24/6). Inthis case, the search space for DCI Format 1A may be composed of 12PDCCH candidates and the search space for each of DCI Formats 1, 2A and2 may be composed of four PDCCH candidates. Similarly, in the case ofMaxBD=18, the number of PDCCH candidates for DCI Format 1A may be 9 andthe search space for each of DCI Formats 1, 2A and 2 may include threePDCCH candidates.

FIG. 11B shows an example of performing PDCCH transmission and BD in thecase of search space sharing. For convenience, it is assumed that searchspaces corresponding to three carriers (or CIF) are constituted. Eachsearch space may correspond to any one of a linked DL CC-UL CC pair, aDL CC or a UL CC. In the drawing, it is assumed that the sizes of threesearch spaces may be different and the CCE aggregation levels of thePDCCH candidates in each search space may be different. For example, asearch space for CC #1 may have a CCE aggregation level of 1 and asearch space for CC #2/#3 may have a CCE aggregation level of 2, 4 or 8.In the drawing, a PDCCH (or PDCCH candidates) (CIF-CC #X) (X=1, 2, 3)may have the same DCI format or different DCI formats.

Case 1 of FIG. 11B shows the case where all search spaces are shared.That is, the PDCCH candidates of the search spaces for CC #1 to #3 havethe same DCI payload size. Since all search spaces are shared, the PDCCHmay be transmitted via PDCCH candidates of any one of the search spacesconstituted per CC. That is, PDCCH candidates may be transmitted via anyone of the search spaces constituted per CC. Referring to the drawing,the PDCCH (CIF=CC #2) is transmitted via the search space for CC #1 andthe PDCCH (CIF=CC #1) and the PDCCH (CIF=CC #3) may be transmitted viathe search space for CC #2. Accordingly, the UE performs BD with respectto the PDCCH candidates of the search spaces for CC #1 to #3 in order tofind the PDCCH (CIF=CC #X)(X=1, 2, 3), on the assumption that the PDCCH(or PDCCH candidates) (CIF=CC #X) (X=1, 2, 3) may be transmitted via thesearch space for CC #1, the search space for CC #2 or the search spacefor CC #3.

Case 2 of FIG. 11B shows the case where the search spaces are partiallyshared. For convenience, it is assumed that the search spaces for CC#1/CC #3 are shared. That is, the PDCCH candidates of the search spacesfor CC #1/CC #3 have the same DCI payload size and the PDCCH candidatesof the search space for CC #2 have a different DCI payload size otherthan the PDCCH candidates of the search spaces for CC #1/CC #3.Referring to the drawing, the PDCCH (or PDCCH candidates) (CIF=CC #3)may be transmitted via any one of the shared search spaces. Accordingly,the UE performs BD with respect to only the PDCCH candidates of thesearch spaces for CC #1/#3 on the assumption that the PDCCH (or PDCCHcandidates) (CIF=CC #3) may be transmitted via the search space for CC#1 or the search space for CC #3. In contrast, in order to confirm thePDCCH (CIF=CC #2), the UE performs BD only with respect to the PDCCHcandidates of the search spaces for CC #2.

FIG. 12 shows a method of constituting PDCCH search spaces if thetransmission modes of DL CCs are set to 1, 1 and 4 under the samecondition as FIG. 11A.

Referring to FIG. 12, the BS constitutes the search spaces per CC andcompares the DCI format sizes for all CCs. As a result of thiscomparison, the sizes of DCI Formats 1A for three DL CCs are the same,the sizes of DCI Formats 1 for two CCs are the same, and only the DCIformat 2 has a different size. Accordingly, the BS unifies the threesearch spaces for DCI Format 1A and unifies the two search spaces forDCI Format 1. Accordingly, the BS may transmit DCI Format 1A (CIF=DL CC#1) via the PDCCH candidate of any one of a search space for DL CC #1, asearch space for DL CC #2 and a search space for DL CC #3. Similarly,the BS may transmit DCI Format 1 (CIF=DL CC #X) (X=1, 2) via the PDCCHcandidate of any one of the search space for DL CC #1 and the searchspace for DL CC #2. In contrast, since DCI Format 2 has a unique size,the search space for DCI Format 2 is not shared and are managed on a perCC basis. That is, DCI Format 2 (CIF=DL CC #3) may be transmitted viathe search space for DL CC #3 alone.

A description will be made in greater detail in consideration of themaximum number MaxBD of times that BD is performed. In the case ofMaxBD=36, the search spaces for the BD of DCI Format 1A include 18(=6×3) PDCCH candidates similar to the example of FIG. 11A. The searchspace of DCI Format 1 may include 12 (=6×2) PDCCH candidates of theunified extended search space and the search space of DCI Format 2 mayinclude six PDCCH candidates. If MaxBD is reduced to 24, the number oftimes that BD is performed per DCI format must be reduced. If it isassumed that the number of times that BD is performed per DCI format iskept constant, the number of times that BD is performed per DCI formatis reduced to 4. In this case, the search spaces for DCI Formats 1A, 1and 2 may be respectively composed of 12, 8 and 4 PDCCH candidates.Similarly, in the case of MaxBD=18, the number of PDCCH candidates forDCI Formats 1A, 1 and 2 may be 9, 6 and 3, respectively.

FIG. 13 is a diagram showing another example of constituting PDCCHsearch spaces. Although the case where only one DL CC is set to a PDCCHmonitoring DL CC is shown in FIGS. 11 to 12, a plurality of DL CCs maybe set to a PDCCH monitoring DL CC set. If the number of CCs within thePDCCH monitoring CC set is L, as shown in FIG. 13, a method of limiting(MaxBD)/L to a maximally allowable number of times that BD is performedper monitoring CC or applying different weights to monitoring CCs (e.g.,anchor DL CCs) (that is, differently limiting the maximally allowablenumber of times that BD is performed per monitoring CC) may be applied.The method of constituting the search spaces according to the number ofmonitoring CCs may be set by the BS in advance or may be automaticallyset by the UE under the MaxBD limitation.

According to the present method, if DCIs (formats) having the same sizeare present upon cross-CC scheduling, the sizes of the search spaces forthe DC's (formats) on the monitoring DL CCs may be set in proportion tothe number of DCIs (formats). Accordingly, it is possible to increase adegree of freedom in PDCCH scheduling and to solve PDCCH blocking.

Embodiment 2: Search Space reduction for cross-CC scheduled PDCCHs

For convenience, a PDCCH transmitted through a specific CC, whichperforms resource assignment with respect to a data channel of thecorresponding CC, is defined as a self-CC PDCCH and a PDCCH, whichperforms resource assignment with respect to a data channel of a CCother than the corresponding CC, is defined as a cross-CC PDCCH. In thiscase, in order to reduce BD times on a specific CC and preferably on aPDCCH monitoring DL CC, both the search space for the self-CC PDCCH andthe search space for the cross-CC PDCCH may be reduced. Preferably, thesearch space for the cross-CC PDCCH is reduced more than the searchspace for the self-CC PDCCH. Alternatively, the search space for theself-CC PDCCH may not be reduced and only the search space for thecross-CC PDCCH may be reduced.

Hereinafter, a description will be made in greater detail with referenceto the drawings. For convenience, in the following drawings, the searchspace for the self-CC PDCCH is not reduced and only the search space forthe cross-CC PDCCH is reduced. However, this is only exemplary and thefollowing drawings and description may be applied to the case where thesearch space for the self-CC PDCCH and the search space for the cross-CCPDCCH are reduced, the case where the search space for the cross-CCPDCCH is reduced more than the search space for the self-CC PDCCH, etc.

FIG. 14 shows an example of constituting PDCCH search spaces if thetransmission modes of DL CCs are 1, 3 and 4 in a state in which three DLCCs are aggregated. For convenience, it is assumed that the bandwidthsof all CCs are the same and DL CC #1 is set to a PDCCH monitoring DL CC.

Referring to FIG. 14, the sizes of DCI Formats 1A for three CCs are thesame and DCI Formats 1, 2A and 2 respectively have unique sizes.Accordingly, the search spaces for DCI Format 1A may be shared. In thedrawing, MaxBD=36 indicates the case where the maximum number of timesthat BD is performed is not reduced. In this case, the number of timesthat BD is performed per DCI format becomes 6 (=36/6) and the searchspaces for DCI Formats 1A, 1, 2A and 2 respectively include 18 (=6×3),6, 6 and 6 PDCCH candidates. In contrast, if MaxBD is reduced to 24, thesearch space for the self-CC PDCCH may be maintained and the searchspace for the cross-CC PDCCH may be reduced. For example, a ratio of thesize of the search space of the self-CC PDCCH to the size of the searchspace of the cross-CC PDCCH per CC (e.g., non-monitoring DL CC) may beset to 2:1. In this case, the search space of the self-CC PDCCH includes12 PDCCH candidates and the search space of the cross-CC PDCCH pernon-monitoring CC includes six PDCCH candidates. Accordingly, the numberof times that BD is performed per DCI format of the monitoring CCbecomes 6 (=12/2) and the number of times that BD is performed per DCIformat of the non-monitoring CC becomes 3 (=6/2). In summary, since DCIFormat 1A is used in the three CCs, the search space includes a total of12 (=6+3+3) PDCCH candidates. In contrast, DCI Format 1 used only in theDL CC #1 (monitoring) may have six PDCCH candidates and DCI Formats 2Aand 2 used only in DL CC #2 and #3 (non-monitoring) may have three PDCCHcandidates.

FIG. 15 shows an example of constituting search spaces for BD of thePDCCH if the transmission modes of the DL CCs are 1, 1 and 4 under thesame condition as FIG. 14. For convenience, it is assumed that thebandwidths of all CCs are the same and DL CC #1 is set to a PDCCHmonitoring DL CC.

Referring to FIG. 15, the sizes of DCI Formats IA for three CCs are thesame, the sizes of DCI Formats 1 for two CCs are the same, and only DCIFormat 2 has a unique size. Accordingly, three search spaces for DCIFormat 1A may be shared and two search spaces for DCI Format 1 may beshared. In the drawing, MaxBD=36 indicates that the maximum number oftimes that BD is performed is not reduced. In this case, the number oftimes that BD is performed per DCI format becomes 6 (=36/6) and thesearch spaces for DCI Formats 1A, 1, and 2 respectively include 18(=6×3), 12 (=6×2) and 6 PDCCH candidates. In contrast, if MaxBD isreduced to 24, the search space for the self-CC PDCCH may be maintainedand the search space for the cross-CC PDCCH may be reduced. For example,a ratio of the size of the search space of the self-CC PDCCH to the sizeof the search space of the cross-CC PDCCH per CC (e.g., non-monitoringDL CC) may be set to 2:1. In this case, the search space of the self-CCPDCCH includes 12 PDCCH candidates and the search space of the cross-CCPDCCH per non-monitoring CC includes six PDCCH candidates. Accordingly,the number of times that BD is performed per DCI format of themonitoring CC becomes 6 (=12/2) and the number of times that BD isperformed per DCI format of the non-monitoring CC becomes 3 (=6/2). Insummary, since DCI Format 1A is used in the three CCs, the search spaceincludes a total of 12 (=6+3+3) PDCCH candidates. Similarly, since DCIFormat 1 is used in the two CCs, the search space includes a total of 9(=6+3) PDCCH candidates. In contrast, the DCI format 2 used only in theDL CC #3 (non-monitoring) may have three PDCCH candidates.

Embodiment 3: Information (e.g., DCI) size unification

In the present method, in order to increase a degree of freedom incontrol channel scheduling, a plurality of control information (e.g.,DCI) formats having different sizes is grouped into a single size. Thatis, DCI size unification (or DCI size matching) may be performed suchthat the DCI formats have the same size. DCI size matching may beperformed only in the case where a difference between the sizes of DCIsis equal to or less than a threshold. For example, DCI size matching maybe performed only in the case where a difference between the sizes ofDCIs is equal to or less than 3 bits. DCI size matching may be performedusing bit padding. A padding bit (stream) may have a specific pattern ora specific value (e.g., 0). For example, the padding bit (stream) mayhave a value indicating a DC1 format or a specific value for errorchecking.

If DCIs (formats) are grouped into a single size, the search spacestherefor may be shared as described in Embodiment 1. Accordingly, thesearch spaces may be extended in proportion to the number of DCIs(formats) grouped into the single size. The use/non-use of the presentmethod and the parameter of the present method may be set by the BS perUE, UE group or cell or may be automatically set by the UE within themaximally allowable number (MaxBD) of times that BD is performed.

FIG. 16 is a diagram showing an example of constituting search spacesfor BD of a PDCCH, if the transmission modes of DL CCs are 1, 3 and 4 ina state in which three DL CCs are aggregated. It is assumed that thebandwidth of DL CC #1 is equal to that of DL CC #2, but is differentfrom that of DL CC #3, and DL CC #1 is set to a PDCCH monitoring DL CC.Accordingly, the sizes of DCI Format 1A for two CCs (DL CC #1 and #2)are the same (Unified F1) and DCI Format 1A (Format 3-1A) for DL CC #3and DCI Formats 1, 2A and 2 respectively have unique sizes. In thepresent example, it is assumed that a threshold for DCI size matching isset to 3 bits.

Referring to FIG. 16, if MaxBD is 36 bits and bit padding is notperformed, the number of times that BD is performed per DCI format is 6and the search spaces for Unified F1 (40 bits), Format 3-1A (44 bits),1-1 (48 bits), 2-2A (53 bits) 3-2 (55 bits) respectively include 12(=6×2), 6, 6, 6 and 6 PDCCH candidates. In contrast, if MaxBD is reducedto 24 and bit padding is performed, the DCI format satisfying thepadding condition (that is, the difference between the sizes of the DCIsis 3 bits or less) is Format 2-2A and Format 3-2 ((Format 3-2: 55bits)-(Format 2-2A: 53 bits)=2 bits<3 bits). Accordingly, Format 2-2A ispadded with 2 bits and Format 2-2A and Format 3-2 may be grouped into asingle size (Unified F2). Since the number of times that BD is performedper DCI format is 4, the search spaces for Unified F1, Format 1-1,Unified F2 and Format 3-1A may respectively include 8 (=4×2), 4, 8(=4×2), 4 PDCCH candidates. As a result, two DCIs (Format 2-2A andFormat 3-2) are grouped into one size, the search spaces, the sizes ofwhich are doubled, are shared, and the degree of freedom in DCIscheduling can be substantially doubled.

FIG. 16 shows the case where the DCI size unification (or DCI sizematching) is performed if the maximum number MaxBD of times that BD isperformed is reduced. However, this is only exemplary and the DCI sizeunification (or DCI size matching) of the present invention isapplicable irrespective of whether or not MaxBD is reduced.

DCI size matching to a single size may be performed even with respect tothree or more DCIs in which a difference between DCI sizes is equal toor below a given threshold. DCI size matching (e.g., bit padding) pergroup may be performed with respect to a plurality of DCI groups. Inaddition, in order to prevent a separate Format Indicator (FI) bit frombeing added, CCs for which DCI formats are set within a DCI group may bemade exclusive. If a plurality of DCI groups is possible, bit paddingmay be preferentially performed with respect to a group having a largernumber of DCI formats or a group having a smaller sum of differenceswith a maximum DCI format size.

In addition, if DCI formats which are commonly set with respect toaggregated CCs are present, the DCI formats are grouped to a single sizewith respect to all CCs or only a part (preferably, one format) of theDCI formats may be grouped to a single size with respect to all CCs.Grouping into a single size includes, for example, bit padding andincrease/decrease in scheduling granularity. In this case, the groupedDCI formats of the CCs may share one search space obtained by unifyingthe search spaces for the DCI formats. In other words, BD for thegrouped DCI formats of the CCs may be commonly performed within oneextended search space. The number of DCI formats commonly set to theaggregated CCs may be one or more.

Although the case in which the present invention is applied to DL CCshas been illustrated thus far, the method of constituting the PDCCHsearch spaces in consideration of UL CCs will now be described indetail. Prior to description, it should be noted that the size of eachsearch space constituted per DL/UL CC pair, DL CC or UL CC may bedetermined in proportion to the maximum number of PDCCHs transmittablevia the search space or may be given weights. For convenience, althoughone DCI format per DL CC or UL CC is set according to transmission modein the following drawing, a plurality of DCI formats (two or more) maybe set. Like DCI Format 0/1A of the conventional LTE system, a DL/ULcommon DCI format may be set.

In the search spaces which consider a DL/UL CC, [Scheme 1] a searchspace for a DL CC and a search space for a UL CC may be independentlyconstituted or [Scheme 2] one search space may be constituted per linkedDL/UL CC pair.

[Scheme 1] Case where the search space for the DL CC and the searchspace for the UL CC are independently constituted

FIG. 17 shows an asymmetric CC aggregation case in which three DL CCsand two UL CCs are aggregated. Referring to FIG. 17, a search space foreach DL CC and a search space for each UL CC may be independentlyconstituted. In this case, DCIs (formats) having the same sizeirrespective of DL/UL may share search spaces corresponding to CCs asdescribed in Embodiment 1. In addition, in order to decrease the numberof times that BD is performed and increase degree of freedom inscheduling, Embodiments 2 and 3 may be applied together/separately.

[Scheme 2] Case where the search space is constituted per linked DL/ULCC pair. The search spaces are constituted per linked DL/UL CC pair. Inthe case of asymmetric CC aggregation in which the number of DL CCs andthe number of UL CCs are different, non-linked CCs may constitute searchspaces per DL CC or UL CC. As a result, the total number of constitutedsearch spaces may correspond to the greater of the total number of DLCCs and the total number of UL CCs. The DL/UL DCIs (formats) having thesame size share search spaces corresponding to CC pairs as described inEmbodiment 1. In addition, in order to decrease the number of times thatBD is performed and increase degree of freedom in scheduling,Embodiments 2 and 3 may be applied together/separately.

1-a) Symmetric CC aggregation case (that is, the number of DL CCs=thenumber of UL CCs): The search spaces are constituted per linked DL/UL CCpair (see FIG. 18).

1-b) DL-heavy CC aggregation case (that is, the number of DL CCs>thenumber of UL CCs): The search spaces are constituted per linked DL/UL CCpair and the search spaces are constituted per DL CC with respect to thenon-linked DL CC (see FIG. 19).

1-c) UL-heavy CC aggregation case (that is, the number of DL CCs<thenumber of UL CCs): The search spaces are constituted per linked DL/UL CCpair and the search spaces are constituted per UL CC with respect to thenon-linked UL CC.

2) If the search space constituted per non-linked CC (DL or UL) istype-A SS and the search space constituted per linked DL/UL CC pair istype-B SS, the size of type-A SS may be equal to or less than that oftype-B SS.

2-a) If it is assumed that a maximum of one PDSCH/PUSCH per CC can bescheduled irrespective of DL/UL, as shown in FIG. 20, since a maximum ofone PDCCH can be transmitted via type-A SS (DL or UL scheduling) and amaximum of two PDCCHs (DL+UL scheduling) can be transmitted via type-BSS, a ratio of the size of type-A SS to the size of type-B SS may be setto 1:2.

3) DCI formats having the same size irrespective of DL/UL share theunified search space as described in Embodiment 1.

4) In order to decrease BD times and increase a degree of freedom inscheduling, Embodiments 2 and 3 may be applied together/separately.

Although, in the present invention, cross-CC scheduling for all DL/ULCCs assigned to the UE from the PDCCH monitoring DL CC is possible,cross-CC scheduling may be set to be performed with respect to a limitednumber of DL/UL CC groups. The setting of the cross-CC scheduling mayvary according to PDCCH monitoring DL CCs. If a plurality of PDCCHmonitoring DL CCs is used, DCIs (formats) having the same size sharecorresponding search spaces on the respective monitoring CCs. If theDCIs (formats) having the same size are present between the monitoringCCs, the corresponding search spaces may be shared. The search spacesmay be shared between the monitoring CCs without limitation in settingof cross-CC scheduling. In order to reduce BD times, the sizes of thesearch spaces shared between the DCIs (formats) having the same size maybe further reduced. For example, if the sizes of the plurality of DCIs(formats) are the same, only a part (one) of the search spaces for theDCIs (formats) may be assigned as the search space shared between theDCIs (formats) or a plurality of search spaces for DCIs (formats) iscollectively reduced so as to constitute one shared search space. Inaddition, the ratio of the size of the search space shared between theDCIs (formats) having the same size may be set in proportion to thenumber of DCIs (formats) sharing the corresponding space.

Simulation

PDCCH blocking probability was evaluated when SS sharing for the samesize DCI formats is applied or not. Simulation assumption is provided inTable 5. CCE aggregation level distribution for PDCCH scheduling (%) isalso provided in Table 6.

TABLE 5 Parameter Assumption BW of PDCCH CC 10 MHz (50 RBs), 20 MHz (100RBs) Total number of CCEs (4Tx DL, 37 (10 MHz), 76 (20 MHz) CIF = 3)CCEs assumed to be occupied by 8 CCEs (out of 16 CCEs) common PDCCHsAggregated CCs (i.e. scheduled 2 CCs PDCCHs) per UE Size of SS at CCEaggregation level 6, 12, 8, 16 CCEs (as in Rel-8) 1/2/4/8 CCEaggregation level for different Independent PDCCHs of a UE DCI formatsize for aggregated CCs Same of a UE Simulation time 50000 subframes SSassignment for each CC Independent (can be overlapped)

TABLE 6 1 CCE 2 CCE 4 CCE 8 CCE 56 29 12 3

FIGS. 21 and 22 show PDCCH blocking probability according to SS sharingwhen 2 CCs are aggregated per UE, and BWs of PDCCH CC are 10 MHz, 20MHz, respectively. As shown in the figures, it is observed that overallPDCCH blocking probability can be largely reduced (more than 25% and 33%reduction in 10 MHz and 20 MHz, respectively) by applying the SS sharingcompared to the case of no SS sharing.

FIG. 23 is a diagram illustrating a base station and a user equipment,which can be applied to the embodiment of the present invention.

Referring to FIG. 23, the wireless communication system includes a basestation (BS) 110 and a user equipment (UE) 120. The base station 110includes a processor 112, a memory 114, and a radio frequency (RF) unit116. The processor 112 can be configured to implement procedures and/ormethods suggested in the present invention. The memory 114 is connectedwith the processor 112 and stores various kinds of information relatedto the operation of the processor 112. The RF unit 116 is connected withthe processor 112 and transmits and/or receives a radio signal. The userequipment 120 includes a processor 122, a memory 124, and a radiofrequency (RF) unit 126. The processor 122 can be configured toimplement procedures and/or methods suggested in the present invention.The memory 124 is connected with the processor 122 and stores variouskinds of information related to the operation of the processor 122. TheRF unit 126 is connected with the processor 122 and transmits and/orreceives a radio signal. The base station 110 and/or the user equipment120 may have a single antenna or multiple antennas.

The aforementioned embodiments are achieved by combination of structuralelements and features of the present invention in a predetermined type.Each of the structural elements or features should be consideredselectively unless specified separately. Each of the structural elementsor features may be carried out without being combined with otherstructural elements or features. Also, some structural elements and/orfeatures may be combined with one another to constitute the embodimentsof the present invention. The order of operations described in theembodiments of the present invention may be changed. Some structuralelements or features of one embodiment may be included in anotherembodiment, or may be replaced with corresponding structural elements orfeatures of another embodiment. Moreover, it will be apparent that someclaims referring to specific claims may be combined with another claimsreferring to the other claims other than the specific claims toconstitute the embodiment or add new claims by means of amendment afterthe application is filed.

The embodiments of the present invention have been described based onthe data transmission and reception between the base station and theuser equipment. A specific operation which has been described as beingperformed by the base station may be performed by an upper node of thebase station as the case may be. In other words, it will be apparentthat various operations performed for communication with the userequipment in the network which includes a plurality of network nodesalong with the base station can be performed by the base station ornetwork nodes other than the base station. The base station may bereplaced with terms such as a fixed station, Node B, eNode B (eNB), andaccess point. Also, the user equipment may be replaced with terms suchas mobile station (MS) and mobile subscriber station (MSS).

The embodiments according to the present invention can be implemented byvarious means, for example, hardware, firmware, software, or theircombination. If the embodiment according to the present invention isimplemented by hardware, the embodiment of the present invention can beimplemented by one or more application specific integrated circuits(ASICs), digital signal processors (DSPs), digital signal processingdevices (DSPDs), programmable logic devices (PLDs), field programmablegate arrays (FPGAs), processors, controllers, microcontrollers,microprocessors, etc.

If the embodiment according to the present invention is implemented byfirmware or software, the embodiment of the present invention may beimplemented by a type of a module, a procedure, or a function, whichperforms functions or operations described as above. A software code maybe stored in a memory unit and then may be driven by a processor. Thememory unit may be located inside or outside the processor to transmitand receive data to and from the processor through various means whichare well known.

It will be apparent to those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

The present invention can be used in wireless communication apparatusessuch as a user equipment, a relay station, a base station and the like.

What is claimed is:
 1. A method of receiving a control channel at a userequipment in a wireless communication system, the method comprising:receiving a subframe including a plurality of search spaces, whereineach of the plurality of search spaces is associated with a respectivecarrier indicator field (CIF) value; and monitoring at least one controlchannel candidate for a cell indicated by a first CIF value in two ormore search spaces of the plurality of search spaces for control channelcandidates having a same downlink control information (DCI) format sizeand different CIF values.
 2. The method according to claim 1, whereinthe two or more search spaces of the plurality of search spaces do notinclude a search space associated with the first CIF value.
 3. Themethod according to claim 1, wherein each of the control channelcandidates further includes a cyclic redundancy check (CRC) scrambled byan identifier.
 4. The method according to claim 3, wherein theidentifier includes a cell radio network temporary identifier (C-RNTI).5. The method according to claim 1, wherein two or more control channelcandidates are discriminated using the different CIF values.
 6. A methodof transmitting a control channel at a base station in a wirelesscommunication system, the method comprising: generating the controlchannel, wherein a carrier indicator field (CIF) value in the controlchannel indicates that the control channel is for a carrier indicated bythe CIF value; and transmitting the control channel in two or moresearch spaces of a subframe, wherein the two or more search spaces arefor control channel candidates having different CIF values and a samedownlink control information (DCI) format size.
 7. The method accordingto claim 6, wherein the control channel further includes a cyclicredundancy check (CRC) scrambled by an identifier.
 8. The methodaccording to claim 7, wherein the identifier includes a cell radionetwork temporary identifier (C-RNTI).
 9. A user equipment for operatingin a wireless communication system, the user equipment comprising: aradio frequency (RF) module; and a processor operably coupled with theRF module and configured to: receive a subframe including a plurality ofsearch spaces, wherein each of the plurality of search spaces isassociated with a respective carrier indicator field (CIF) value, andmonitor at least one control channel candidate for a first cellindicated by a first CIF value in two or more search spaces of theplurality of search spaces for control channel candidates havingdifferent CIF values and a same downlink control information (DCI)format size.
 10. The user equipment according to claim 9, wherein thetwo or more search spaces of the plurality of search spaces do notinclude a search space associated with the first CIF value.
 11. The userequipment according to claim 9, wherein each of the control channelcandidates further includes a cyclic redundancy check (CRC) scrambled byan identifier.
 12. The user equipment according to claim 11, wherein theidentifier includes a cell radio network temporary identifier (C-RNTI).13. The user equipment according to claim 9, wherein two or more controlchannel candidates are discriminated using the different CIF values. 14.A base station for use in a wireless communication system, the basestation comprising: a radio frequency (RF) module; and a processoroperably coupled with the RF module and configured to: generate acontrol channel, wherein a carrier indicator field (CIF) value in thecontrol channel indicates that the control channel is for a carrierindicated by the CIF value, and transmit the control channel in two ormore search spaces of a subframe, wherein the two or more search spacesare for control channel candidates having different CIF values and asame downlink control information (DCI) format size.
 15. The basestation according to claim 14, wherein the control channel furtherincludes a cyclic redundancy check (CRC) scrambled by an identifier. 16.The base station according to claim 14, wherein the identifier includesa cell radio network temporary identifier (C-RNTI).